The biochemistry and biophysics of amine storage in pig and human platelets have been studied by nuclear magnetic resonance spectroscopy. Amine storage does not appear to be the result of the formation of a macromolecular complex, but rather involves relatively close packing of amine molecules in interstices provided by other vesicle constituents. Examination of model systems indicates the technique will be useful for continued study of amine storage, as well as of the effects of psychoactive drugs and lithium on this process.